The present invention relates to a low-pass filter for use at a user end or office end in a communication network, and more particularly to a bi-directional low-pass filter for use at a user end or office end in a communication network.
In order to enhance the data transmission rate in the internet, various techniques for broadband linkage are developed. For example, Digital Subscriber Line (DSL) uses copper wires common to general users to perform high-speed data transmission. Nowadays, many different versions of DSL techniques have been derived, and they are generally known as xDSL. Among them, the most popular one, so far, is Asymmetric Digital Subscriber Line (ADSL).
Please refer to FIG. 1 which is a schematic diagram showing the application structure of ADSL. As shown, voice grade terminals 11 such as telephone sets or fax machines, and a remote terminal end 12 of an ADSL transceiver unit (ATU-R) share a conventional telephone line 10 to perform transmission therefor. The telephone line 10 is connected to a central office end 14 via a network interface device (NID) 13.
In general, ADSL utilizes a high frequency band, e.g. 25 kHz to 1 MHz, of the telephone line 10 to transmit information in the internet. Therefore, in principle, a low frequency band, e.g. a voice band, of the telephone line 10 can be provided for the voice grade terminals 11 to make a phone call or fax. In practice, however, the signal in the high frequency band may interfere with the signal in the low frequency band so as to adversely effect the telephone or facsimile communication quality relating to attenuation values. In order to solve this problem, low-pass filters 111 are provided between respective voice grade terminals 11 and the telephone line 10. The circuit of each low-pass filter 111 is optionally arranged inside or outside the housing of the corresponding voice grade terminal 11. FIG. 2 shows a circuit diagram of a conventional low-pass filter.
As shown in FIG. 2, it is clear that the conventional low-pass filter has to be mounted in a designated direction, i.e. input from the telephone line, and output to the voice grade terminal. If the filter is mounted incorrectly, the overall transmission efficiency of the network will be lowered.
Therefore, an object of the present invention is to provide a low pass filter which can be operated reversibly.
Another object of the present invention is to provide a low pass filter which has a satisfactory attenuation property in high-band.
The present invention relates to a low-pass filter for use in a communication network. The communication network includes a high-band communication terminal, a low-band communication terminal, and a signal channel common to the high-band and low-band communication terminals. For example, the communication network may include a home PNA client as the high-band communication terminal, a voice grade terminal as the low-band communication terminal, and a telephone line as the signal channel.
A first aspect of the present invention relates to a bi-directional low-pass filter which includes a first, a second, a third and a fourth input/output ends; a first, a second, a third and a fourth inductors electrically connected to the first, second, third and fourth input/output ends, respectively; a first capacitor having a first and a second ends; a fifth, a sixth, a seventh and an eighth inductors arranged in a manner that the fifth and sixth inductors are electrically connected to the first and second inductors, respectively, and further to the first end of the first capacitor in series, and the seventh and eighth inductors are electrically connected to the third and fourth inductors, respectively, and further to the second end of the first capacitor in series; and a first, a second, a third and a fourth compensation circuits electrically connected to the fifth, sixth, seventh and eighth inductors in parallel, each of the compensation circuits including a compensation capacitor and a compensation resistor interconnected in series.
A second aspect of the present invention relates to a bi-directional low-pass filter which includes a first, a second, a third and a fourth input/output ends; a first, a second, a third and a fourth inductors electrically connected to the first, second, third and fourth input/output ends, respectively; a first capacitor having a first and a second ends; a fifth, a sixth, a seventh and an eighth inductors arranged in a manner that the fifth and sixth inductors are electrically connected to the first and second inductors, respectively, and further to the first end of the first capacitor in series, and the seventh and eighth inductors are electrically connected to the third and fourth inductors, respectively, and further to the second end of the first capacitor in series; a first, a second, a third and a fourth compensation circuits electrically connected to the fifth, sixth, seventh and eighth inductors in parallel, each of the compensation circuits including a compensation capacitor and a compensation resistor interconnected in series; and a first, a second, a third and a fourth high-band attenuation circuits electrically connected to the compensation resistors of the first, second, third and fourth compensation circuits in parallel, respectively, each of the high-band attenuation circuits including a high-band attenuation inductor and a high-band attenuation resistor.
The first and the fourth input/output ends are electrically connected to the signal channel, and the second and third input/output ends are electrically connected to the low-band communication terminal. Alternatively, the first and the fourth input/output ends are electrically connected to the low-band communication terminal and the second and third input/output ends are electrically connected to the signal channel.
Preferably the first, fifth, eighth and fourth inductors are wound around a first core, and the second, sixth, seventh and third inductors are wound around a second core.
Preferably, an inductance of each of the first, second, third and fourth inductors is 0.5 mH, and an inductance of each of the fifth, sixth, seventh and eighth inductors is 0.75 mH. A capacitance of the compensation capacitor is ranged between 1000 pf and 35 nf, and a resistance of the compensation resistor is ranged between 10 xcexa9 and 10 kxcexa9. A capacitance of the first capacitor is ranged between 4.7 nf and 22 nf. An inductance of the high-band attenuation inductor is ranged between 300 xcexcH and 2.0 mH, and a resistance of the high-band attenuation resistor is ranged between 10 xcexa9 and 1 kxcexa9.